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r     %  2  3 

4  5  6 


■> 


A  NORTH  AMERICAN 

SEA  OF  JURASSIC  AGE 


A  pISSERtATIOK  SUfilHTTlD  TP  THB   PACWtTllBS  PF  TH«  OfcAOUATE 

SCHPOL8  pf  ARTS,  |.lTgitATOItB,  AND  SCWNCB,  IN   CAlf&iQACV 

fPlk  THB  DSPRBB  P7  DPCTPB  P»  PHlLPSPT-HV 

DBPARTMIMT,  0»  GIOLOOY 


BV 


WILLIAM   NEWTON  LOGAN 


e»fl0AG6 


^- 


Uhc  Tanfverstti?  of  Cbfcago 

FOUNDED  BV  JOHN  D,  ROCKKFKLLBH 


A  NORTH  AMERICAN  EPICONTINENTAL 
SEA  OF  JURASSIC  AGE 


A    DISSERTATION    SUBMITTED   TO    THE    FACULTIES    OF    THE    GRADUATE 

SCHOOLS    OF  ARTS,  LITERATURE,  AND   SCIENCE,  IN    CANDIDACY 

FOR    THE    DEGREE    OF    DOCTOR    OF    PHILOSOPHY 


DEPARTMENT   OF   UEOI.OGY 


WILLIAM    NEWTON    LOGAN 


«>  CO  / 


X 


.S.OF  "^^ 


.L  83 


RKHRINTK.n   FROM 

Sbe  journal  of  Geology 

AI'RIL-MAY,  IQOO 

P. 

PuW. 

290  'Ui 

■  f 


A  NORTH  AMERICAN  EPICONTINENTAL  SEA  OF 

JURASSIC    AGE 

I,  Introduction. 

I.  Statement  of  the  lines  of  investigation. 
II.  Nature  and  extent  of  the  sea. 

1.  Present  known  distribution  of  the  deposits. 
a')  South  Central  Wyoming  area. 

d')  Southeastern  Idaho  area. 
c')  Northern  Uinta  area. 
ei')  Southern  Uinta  area. 
e')  Southern  Utah  area. 
/)  Black  Hills  area. 
£■' )  Montana  area. 
A')  Canadian  area. 
/')  Aleutian  area. 

2.  Conclusions. 

III.  Relation  of  the  interior  fauna  to  the  northern  Eurasian  fauna. 

IV.  Connection  of  the  sea  with  the  ocean 

V.  Lfck  of  communication  between  the  Californian  province  and  the  interior, 
and  the  causes  assigned. 

1.  The  climatic  hypothesis. 

2.  An  alternative  hypothesis. 
General  conclusions. 


VI 


INTRODUCTION 


The  following  line  of  investigation  is  the  out-growth  of  the 
study  of  the  faunal  and  stratigraphical  conditions  as  they  are 
expressed  in  the  Jurassic  formation  of  the  Freeze-Out  Hills  in 
southern  Wyoming.'  In  making  these  investigations  the  writer 
has  been  led  to  test,  in  the  light  of  new  doctrines'  and  moi- 
recent  observations,  certain  prevalent  opinions  bearing  on  Juras- 
sic faunal  geography.  In  connection  with  these  investigations 
there  arose  also  questions  concerning  which  no  definite  statement 

■Logan  :  Kansas  Uni.  Quart.,  April  1900. 

•See  papers  by  Dr.  T.  C.  Chamberlin  on  :  "A  Source  of  Evoiution  of  Provin- 
cial Faunas,"  JouR.  Geol.,  Vol.  VI,  p.  598  ;  "  The  Ulterior  Basis  of  Time  Divisions," 
Hid.,  p.  449. 

241 


I.IIIHIII.IIIIIW 


■ 


242 


fr.  A^  LOGAN 


of  opinion  has  as  yet  appeared  in  our  geological  literature. 
Among  the  lines  of  investigation  which  suggested  themselves 
were  the  following:  (i)  The  nature  and  extent  of  the  intenor 
Jurassic  sea;  (2)  the  relation  of  the  interior  fauna  to  other 
faunas-  (3)  the  connection  or  connections  of  the  sea  with  the 
ocean;'  and  (4)  the  causes  for  the  lack  of  communication 
between  the  Interior  province  and  the  Californian  faunal  prov- 


mv;e. 


Some  of  these  questions,  notably  the  second  and  fourth,  have 
already  received  a  somewhat  exhaustive  discussion  at  the  hands 
of  a  number  of  geologists.  In  the  majority  of  cases,  however, 
the  conclusions  formed  have  been  connected  with  certa.n  funda- 
mental assumptions  concerning  the  validity  of  which  there  is  at 
present  profound  skepticism.  As  these  new  doctrines  are  more 
or  less  intimatelv  associated  with  new  fundamental  hypotheses, 
a  test  of  the  one  is  in  a  measure  a  test  of  the  other ;  but  a  dis- 
cussion of  original  postulates  does  not  fall  primarily  within  the 
province  of  this  investigation.  Therefore  the  discussion  will  pro- 
ceed along  the  lines  already  indicated  and  in  the  order  above 

mentioned. 

Nature  and  extent  of  the  sea.-\vi  order  to  present  the  data 
upon  which  our  conclusions  concerning  the  nature  and  extent 
of  the  Jurassic  sea  are  based  it  wiU  be  necessary  to  give  a  sum- 
mary of  the  stratigraphical  and  faunal  conditions  of  the  present 
known  Jurassic  areas.  In  collecting  this  data  I  have  consulted 
the  writings  of  a  long  list  of  geologists  who  have  labored  in  this 
particular  geological  field.'  On  the  whole  it  may  be  said  that 
the  results  obtained  by  these  men  are  strikingly  harmonious ;  so 
that  no  grave  difficulty  should  be  met  in  any  attempted  logical 
interpretation  of  the  facts.  .  .  .    r  1 

These  Jurassic  areas  will  be  discussed  in  the  order  which  fol- 
lows •  (i)  The  South  Central  Wyoming  area ;  (2)  the  Southeast- 
ern Idaho  area  ;  (3)  the  Northern  Uinta  area;  (4)  the  Southern 
Uinta  area;  (5)  the  Southern  Utah  area;  (6)  the  Black  Hills  area; 
(7)  the  Montana  area;  (8)  the  Canadian  area;  (9)  the  Aleutian 

»  For  references  see  following  discussion. 


EPICONTINENTAL  SEA  OF  JURASSIC  AGE 


243 


area.  Many  of  these  terms  have  been  used  in  a  loose  ^rcojrraphic 
sense  since  the  object  is  to  include  under  one  name  all  of  the 
minor  localities  belonging  to  one  areal  province.  The  numbers 
on  the  map'  indicate  the  position  of  these  areas 

THE    SOUTH    CENTRAL    WYOMING    AREA 

The  Freeze-Out  Hills. '-l\\t  oldest  rocks  recognized  in  the 
Freeze-Out  Hills  are  the  Carboniferous.  They  occupy  the  cen- 
ter of  the  partly  dissected  anticline  and  are  overlain  by  the  Red 
Beds  which  are  composed  of  sandstones  and  reddish  arenaceous 
clays  and  marls  inclosing  here  and  there  lenticular  masses  of 
gypsum  or  gypsiferous  clays.  These  beds  are  seemingly  devoid 
of  fossils  and  are  apparently  conformable  with  the  overlying 
Jurassic  beds  of  unquestionable  marine  deposition.  At  a  point 
on  the  Dyer  Ranch  the  following  stratigraphical  conditions  of 
the  contact  between  the  Red  Beds  and  the  Jura  were  noted  in 
ascending  order  -.^ 

1.  Base,  near  top  of  the  Red  Beds,  reddish  clay,  2'-f  ; 

2.  White,  indurated  sandstone,  4" ; 

3.  Clay,  light  red,  5"; 

4.  White  sandstone  with  a  reddish  tinge,  i'; 

5.  Light  red  clay,  2" ; 

6.  White,  slightly  indurated  sandstone,  6' ; 

7.  Shale   reddish  changing  to  purple,  4'  ; 

8.  White  fissile  arenaceous  limestone,  6'  ; 

9.  Arenaceous  clay  of  a  dull  red  color,  10'  ; 

10.  White  laminated  arenaceous  limestone  containing  fossils, 

6'. 

This  last  stratum  contains  a  characteristic  Jurassic  type, 
Pseudomonotis  curta  Hall.  This  is  the  first  or  lowest  known  fossil 
bearing  horizon  of  the  Jura  in  this  area.  Any  division  line 
between  the  Red  Beds  and  the  Jura  placed  lower  than  this  fossil 
bearing  stratum  would  be  an  arbitrary  one  as  there  appears  to 
be  no  unconformity  to  mark  the  separation.  To  the  beds  occur- 
ring above  the  fossiliferous   horizon  the  term   Jura -Trias  is  no 

I  See  p.  245.  '  Logan  :  Kansas  Uni.  Quart.,  April  1900. 

3  Quoted  from  paper  mentioned  above. 


•HWW 


244 


J^'.  .V.  LOG  AN 


lonjrcr  applicable  as  they  arc  utKiucstionably  Jura.     As  the  Red 
Hcds  represent  the  whole  interval   of   time   from   the  Carbonif- 
erous to  the  Jurassic  so  far  as  evidence  to  the  contrary  is  con- 
cerned the  term  Jura-Trias  alone  is  not  applicable  to  them. 
Continuing  the  section  already  begun  we  have  for  number 
1  I.  Arenaceous  clay  of  a  somewhat  shaly  nature,  6'.     This 
layer  contains  near  the  central  horizon  a  more  highly  arenaceous 
stratum  of  greenish  color.   It  has  scattered  through  it  at  different 
levels  some  rather  large  brown  argillaceous  concretions.     The 
entire  stratum   seems  to  be  unfossiliferous  but   it   may  contain 
Belemmtcs  densus  as  it  is  often  difficult  to  determine  whether  this 
fossil  does,  or  does   not,  belong   to   the  lower  beds,   since,   on 
account   of  its  abundance  in  the   ui)per  beds,  it  is  usually  scat- 
tered superficially  throughout  the  full  extent  of  the  outcrop. 

12.  White  sandy  clay,  4'-  No  invertebrate  fossils  were 
found  in  this  stratum  but  the  remains  of  marine  saurians  belong- 
ing to  the  genera.  Ichthyosaurus  and  Plesiosaurus  occur  in  consid- 
erable abundance. 

13.  Purplish  fossiliferous  clay  containing  calcareous  nodules, 
20'.     The    most    abundant   fossil   in    this   stratum  h  Be/emni(i'S 
densus  which  occurs  distributed  throughout  the  layer  while  the 
other  fossils  are  confined  chiefly  to  calcareous  concretions.     From 
these  concretions  the  following   forms  were  obtained:     Pinna 
kingi  Meek;  Cardiocerasf  cordiforme  M.  &   H.;  Belemnites  densus 
M.&  H.;  Astericus pentiicrinus  M.  &   H.;  Astarte packtirdi  \Nhhe; 
Pleuromya  subcompressa  White ;    PseudomonoHs  curta  Hall ;   Tan- 
credia  bullosa  White;    Goniomya  montanaensis  Meek;    Tancredia 
magna  Logan ;  Lima  lata  Logan ;  Belemnites  curta  Logan ;  Car- 
dinia   wyomingensis   Logan    and    AviciUa    beedei    Logan.      This 
stratum  contains  also  the  remains  of  Plesiosaurs  and  Ichthyosaurs. 
It  is  the  most  abundantly  fossiliferous  of  the  entire  series.     It  is 
also  one  of  the  most  persistent  beds,  and  is  everywhere  charac- 
terized by  the  great  abundance  of  Belemnites. 

14.  Greenish  colored  sandstone  separating  into  thin  layers, 
2'  to  4'.  This  stratum  is  very  persistent,  contains  considerable 
calcareous  matter,  and  is  easily   recognized  on  account  of  its 


EPlCOXriXKXTA/.  SKA   or  JURASSIC  AGE 


MS 


Fig.  I. — Map  showing  the  distribution  of  the  Jurassic  formation  in  the  interior. 


240 


/K  A^.   LOGAN 


uniformly  greenish  color.  The  following  fossils  occur  in  it: 
CampUmcctes  bcllistriatiis.  Meek;  Camptoncctcs  exteimatus  M.  &  H.; 
Gryphca  calceola  var.  nebrasccnsis  M.  &  H.;  Oitrea  stngilecula 
White  and  Ostrea  densa  Logan. 

15.  Purplish  clay  containing  considerable  arenaceous  inclu- 
sions, 40'.  The  clay  contains  in  the  upper  part  a  thin  strata  of 
sandy  limestone  in  which  the  following  fossils  were  found : 
Pentacrinus  astcricns  M.  &  H.;  Asterias  duhium  White;  Psctidomo- 
notis  ciirta  Hall ;  AviaUa  macrotiatus  M.  &  H.;  and  Ostna  strigile- 
cula  White. 

Como  beds. — The  last  stratum  is  the  uppermost  one,  containing 
marine  fossils  and  probably  closes  the  Jura.  The  succeeding 
layer  varies  so  much  in  thickness  within  short  distances  that  it 
may  represent  the  slightly  eroded  surface  upon  which  the  Como 
beds  were  deposited. 

16.  Fine-grained,  grayish-white  sandstone,  10' to  125'.  The 
above  stratum  varies  much  in  thickness  withui  short  distances. 
At  one  point  on  the  Dyer  Ranch  it  has  a  thickness  of  lo',  while 
a  few  miles  southeast  of  that  point  it  reaches  a  thickness  of  125'. 
The  sandstone  composing  the  layer  is  of  nearly  uniform  color 
and  texture.  Its  induration  is  only  moderate,  and  it  weathers 
into  many  grotesque  forms.  Cross-bedding  is  well  exhibited  by 
it  in  many  localities. 

17.  Purple  to  greenish  colored  clay,  60'.  This  is  apparently 
an  unfossiliferous  layer  except  in  the  uppermost  horizon,  where 
species  of  Dinosaurs  belonging  to  the  genera  Brontosaurus  and 
Morosaurus  occur.  This  is  the  lowest  fossiliferous  horizon  of  the 
Como  beds  and  the  beds  included  between  this  horizon  and  the 
layer  marked  1 5  may  represent  the  transition  from  marine  to 
non-marine  conditions. 

18.  Sandstone,  grayish  to  light  brown,  10'  to  20'.  The 
above  sandstone  presents  some  very  interesting  stratigraphical 
phenomena.  It  has  at  the  base  a  layer  of  conglomerate  about 
2>^'  thick.  The  conglomerate  is  composed  of  small  argiUa- 
ceous  and  silicious  pebbles,  and  is  not  very  coherent.  Something 
like  two  feet  of    sandstone   rest   upon   the   conglomerate;    the 


ffcifeiWiiiiiaiiiniJ'r'nir 


EPICONTINENTAL  SEA   OF  JURASSIC  AGE  247 

bedding  planes  of  the  sandstone  are  oblique  to  the  beds  above 
and  below.  Succeeding  the  sandstone  above  is  6"  of  sandstone 
in  very  thin  layers,  with  lignitic  seams  along  its  horizontal  but 
wavy  bedding  planes.  The  above  is  overlain  by  4"  of  conglom- 
erate followed  by  I '  of  sandstone  with  oblique  bedding  planes. 
Overlying  this  layer  is  a  thin  layer  of  sandstone  in  which  the 
bedding  planes  are  horizontal.  The  remainder  of  the  stratum  is 
made  up  of  sandstones  with  the  thicknesses  and  bedding  planes 
as  follows:  i'  oblique;  3"  horizontal;  2'  oblique;  and  finally  3' 
horizontal. 

The  beds  furnished  in  one  place  the  trunk  of  a  large  fossil 
tree  and  a  large  number  of  fossil  cycads.  Fragments  of  wood 
were  found  in  a  number  of  places,  but  cycads  in  only  the  one. 
Fragments  of  a  hollow-boned  Dinosaur  were  secured  from  one 
place  in  the  horizon. 

19.  Drab-colored  clay,  30'  to  40'.  This  stratum  contains 
the  remains  of  Brotitosaurus  and  Morosaimis.  Otherwise  it 
appears  to  be  unfossiliferous. 

20.  Fissile,  brownish  sandstone,  4'  to  5'.  No  fossils  were 
found  in  this  sandstone,  and  a  most  characteristic  feature  about 
it  is  its  uniformly  brown  color.  It  seems  to  be  moderately  per- 
sistent, as  it  was  noticed  in  many  places  in  the  hills. 

2 1 .  Bluish-green  clay,  containing  very  small  concretions,  30 ' . 
In  the  bone  quarries  of  this  horizon,  which  furnished  species  of 
Brotitosaurus,  Morosaurus  and  Diplodocus  were  found  specimens  of 
Lioplacodes  {Planorbis)  veternus  Meek,  and  Valvata  leei  Logan. 
This  is  the  lowest  horizon  at  which  any  of  these  non-marine 
invertebrates  were  noticed.  It  is  very  probable  that  they  will 
be  found  in  the  beds  below  as  they  indicate  similar  conditions  of 
deposition. 

22.  Brown  to  bluish-gray  arenaceous  limestone,  8'  to  i'. 
This  stratum  contains  the  following  non-marine  invertebrate 
forms  :  Unio  knighti  Logan  ;  Utiio  willistoni  Logan  ;  Unio  baileyi 
Logan  ;  Valvata  leei  Logan  ;  and  Lioplacodes  {Planorbis)  veternus 
Meek.  Species  of  the  same  genera  have  been  described  by 
Meek  from  a  similar  stratum  of  limestone   in  the   Black  Hills. 


il<ft*itwBi— HJmUBgafteWMi 


<rs*.**i<t3HMv^:l»«*»'*»-i:^4W»w*'yA/aM.?-*-f*y''" 


■  '^J'TaM."-^-^- 


248 


IV.  N.  LOGAN 


As  these  occu|)y  much  the  same  stratigraphical  position  they  are 
very  likelv  of  the  same  age.  The  Lioplacodes  seems  to  be  identi- 
cal with  that  described  by  Meek  in  the  Geology  of  the  Upper 
Missouri. 

23.  Drab-colored  clay,  70'.  Species  of  the  genera  Bronto- 
saunis,  Diplodocus,  Morosaurus,  Stegosaunis  and  Allosaurus  occur 
in  this  horizon.  Portions  of  species  of  all  these  genera  were 
found  in  one  quarry  by  the  Kansas  University  collecting  party  of 
which  the  writer  was  a  member.  The  clay  is  of  that  quality 
usually  designated  as  joint  clay.  It  contains,  in  places,  iron  and 
argillaceous  concretions  of  small  size.  The  iron  and  sometimes 
the  bones  are  covered  with  small  selenite  crystals. 

24.  Grayish-white  sandstone,  50'.  This  layer  forms  a  con- 
spicuous capping  for  the  hills,  and  is  the  highest  remnant  of  the 
anticline.  It  breaks  up  into  large  blocks,  which  lie  scattered 
along  the  slopes  of  the  underlying  softer  beds.  Its  erosion  and 
disintegration  is  accomplished  chiefly  by  sapping.  No  fossils 
were  found  in  this  stratum"  (Dakota?). 

The  maximum  thickness  of  the  Jura  for  this  locality  does 
not  at  the  most  exceed  lOO  feet.  All  of  the  fossils  are  found  in 
a  vertical  range  of  but  little  more  than  half  that  distance,  and 
yet  the  fauna  includes  all  the  characteristic  species  of  the 
interior  Jurassic  province.  The  beds  are  heterogeneous  and 
indicate  constantly  varying  conditions  of  sedimentation. 

The  entire  section  is  given  in  its  minutest  details  so  that  an 
idea  of  the  general  character  of  the  Como  beds  may  be  obtained. 
In  many  localities  this  formation  has  been  included  in  the  Jura, 
although  the  Jura  is  wholly  marine  while  on  the  other  hand  the 
Como  is  wholly  fresh  water.  On  the  whole  the  marine  beds  are 
more  calcareous  but  there  is  usually  at  least  one  thin  bed  of 
limestone  in  the  Como.  The  lithological  characters  of  the  beds 
do  not  always  stand  out  so  clearly  that  the  evidence  of  fossils 
is  not  required  to  separate  the  beds. 

Como  Lake? — The  stratigraphical  conditions  of  the  formation 
at  Lake  Como  are  not  essentially  different  from   those  of  the 

'Logan  :  loc.  cit. 


EPICONTINENTAL  SEA   OF  JURASSIC  AGE 


249 


Freeze-Outs.  The  beds  have  the  same  lithological  character- 
istics, being  composed  of  sandstones,  arenaceous  clays,  marls 
and  impure  limestones.  They  rest  on  the  Red  Beds  and  are 
overlain  by  about  the  same  thickness  of  the  Como  (Atlanta- 
saurus)  beds.  The  latter  formation  is  capped  by  an  apparent 
continuatio.i  of  the  same  quartzitic  layer  which  forms  the  surface 
stratum  in  the  F^reeze-Outs.  From  this  area  the  following  spe- 
cies have  been  determined  by  the  writer  and  others  :  Asterias 
dubium;  Pentacritms  astericus ;  Belemnites  densus;  Cardioceras? 
cordiforme ;  Pscudomonotis  curta;  Camptonectes  bellistriatus ;  Ostrea 
strigileada ;  Ostrea  comoensis;  Phma  kingi;  Tancredia  inornata; 
Plenromya  subcompressa ;  Astarte  packardi;  and  Goniomya  montan- 
aensis. 

Rawl'ms  Peak. — The  Jurassic  at  this  point  exhibits  about  the 
same  thickness  and  lithological  characters  as  that  of  the  Como 
area.  The  beds  contain  the  following  forms  :  Camptonectes  bel- 
listriatus; Belemnites  dctisus;  Astarte  packardi;  Pseudomotwtis  curta; 
Ostrea  strigilecula ;  and  Pentacrinus  astericus. 

Sweetwater. — In  the  Sweetwater  Drainage  area  Endlich  '  gives 
300  feet  as  the  thickness  of  the  jura  at  that  place  and  states  that 
it  contains  a  Gryphea  and  a  Belemnites. 

East  of  the  Wind  River  Range  according  to  the  same  writer ' 
the  Jura  has  a  thickness  of  200  or  220  feet  and  consists  at  the 
base  of  dark  calcareous  shales,  covered  by  beds  of  dark  blue  lime- 
stones. These  are  followed  by  yellow  shales  and  marls  with 
intercalations  of  thin  sandstone  layers.  Yellow,  pink  and  green- 
ish marls  close  the  section.  The  fossils  obtained  are  species  of 
Belemnites,  Gryphea,  Rhynchonella,  Lingula,  Modiola,  Pecten,  and 
others. 

THE    SOUTHEASTERN    IDAHO    AREA 

In  this  area  St.  John^  places  the  thickness  of  the  Jura  at 
2000  feet.  Since,  however,  only  the  lowermost  beds  are  fossil- 
iferous  it  is  probable  that  the  Jura  should  be  restricted  to  that 

'  Ann.  Rep.  U.  S.  Geol.  Surv.,  Vol.  XI,  1877,  p.  108. 

»/*i</.  p.  87. 

3  Ann.  Rep.  U.  S.  Geol.  Surv.,  Vol.  XI,  1877,  p.  495. 


mmMtmmmmmmumm 


.4^ 


250 


M^.  A',  LOGAN 


horizon.  The  beds  consist  here  as  elsewhere  of  alternating  beds 
of  sandstone,  shales,  and  limestones. 

In  the  Lincoln  Basin  the  following  Jurassic  fossils  were  col- 
lected :  Ostrea  strigilecula ;  Belemnites  densus;  Pentacrinus,  Ostrea, 
Grypliea,  Comptoncctes,  and  Psctidomonotis. 

At  Meridian  Ridge  Peale '  found  i  50  feet  of  bluish  and  gray 
limestones  ;  bluish  laminated  limestones  and  bluish  argillaceous 
shales  and  slates  followed  by  1 00  feet  of  reddish  sandstone  and 
bluish  limestone  containing  Pentacrinus  astericus;  Ostrea  strigilec- 
ula; Camptonectes  bellistriattis  and  other  forms.  This  thickness  of 
250  feet  doubtless  represents  a  conservative  average  for  the 
entire  district. 

On  the  John  Day  (Gray)  River"  the  following  fossils  were 
collected  :  Pentacrinus  astericus ;  Belemnites  densus;  Camptonectes 
bellistriattis ;  Gryphea,  Trigonia,  and  Pleuromya ;  and  from  another 
outcrop,  Pentacrinus  astericus;  Ostrea  strigilecula,  and  Tancredia  sp. 
An  outcrop  in  the  Sublette  Range  furnished  Pentacrinus  astericus 
and  Camptonectes  bellistriattis. 

The  Jura  at  Bear  Lake  Plateau'  contains  Psetidomonotis  ctirta 
and  other  forms.  The  fossiliferous  beds  consist  of  90  feet  of 
gray  limestone  and  80  feet  of  bluish-gray  limestone  with  bands 
of  sandstone.  This  group  rests  on  150  feet  of  limestone  which 
may  also  be  Jura  but  there  is  no  faunal  evidence  of  its  age. 

On  Bear  River  in  Southwestern  Wyoming  Meek*  gives  the 
following  section  for  the  Jura  :  "  Ferruginous  sandstone,  in  thin 
layers,  dipping  northwest  about  80°  below  horizon,  40  feet; 
bluish  laminated  clays  with,  at  top  (left  cr  west  side),  a  two- 
foot  layer  of  sandstone  containing  fragments  of  shells  not  seen 
in  a  condition  to  be  determined,  125  feet ;  Clays  and  sandstones, 
below  (20  feet);  gray  and  brown  pebbly  sandstone  above  (25 
feet),  45  feet;  brownish  and  bluish  clays,  with  some  beds  of 
white,  greenish,  and  brown  sandstone,  115  feet."  From  the 
second    layer   the    following   fossils  were  obtained :    Belemnites 

'  Ann.  Rep.  U.  S.  Geol.  Surv.,  Vol.  XI,  1877,  p.  536- 

o/ii,/.  p.  544.  3/fiiJ.  p.  585. 

« Ann.  Kept.  U.  S.  Geol.  Surv.,  Vol.  VI,  1872,  p.  451. 


V'/^*4^t55r 


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EPICONTINENTAL  SEA   OF  JURASSIC  AGE 


251 


dinsus,  Trigonia  QiiadriiHgularis,  and  Plcuromya  wehcrcusis  ?  This 
stratum  of  125  feet  is  all  of  the  section  th^t  can,  with  certainty, 
be  assigned  to  the  Jura,  as  the  other  layers  are  unfossiliferous. 

The  third  and  fourth  layers  correspond  in  character  to  the 
Como  beds  in  other  areas  in  Wyoming. 

V       !^  THE    NORTHERN    UINTA    AREA  . 

Flaming  Gorged — In  the  Flaming  Gorge  the  total  thickness 
of  the  Jurassic  is  placed  at  700  feet.  Three  hundred  feet  near 
the  middle  of  the  outcrop  contains:  Catnptoucctes  bellistriatHs ; 
Gryphea  calccola;  Pcutacrinus  astericus ;  Rynchonella  guathophora ; 
Trigonia  americatm,  Trigonia  conradi;  Ostrea  strigileciila ;  and  Belem- 
nites  demus.  In  the  absence  of  fossil  evidence  the  portion  of  the 
outcrop  lying  above  and  below  this  horizon  cannot  with  cer- 
tainty be  assigned  to  the  Jura.  Therefore  it  is  possible  that  the 
three  hundred  feet  represents  the  whole  thickness  of  the  Jura 
for  this  area. 

South  of  Dead  Man's  Springs  calcareous  beds  which  are 
thought  to  represent  the  middle  part  of  the  Jura  for  that  area 
contain  :  Camptonectes  bellistriatus ;  Myoplwria  lineata ;  Gryphea  cal- 
ceola;  and  Pentacrintis  astericus. 

Vermillion  Cliffs.'' — From  Vermillion  Cliffs  in  Northwestern 
Colorado  White  determined  the  following  Jurassic  species: 
Belemnites  densus;  Cardioccras,  cordiforme ;  Pentacriyius  astericus; 
Rhynchonella  gnathophora ;  Rhynchotiella  myrina;  Ostrea  strigile- 
cula;    Ostrea  procumbens ;  and  Modiola  subtmbricata. 

The  limits  of  the  Jurassic  sea  in  a  southeasterly  direction  do 
not  appear  to  have  been  far  from  this  point.  Northwestern 
Colorado  has  up  to  this  time  been  the  only  part  of  the  state  to 
which  unquestionable  Jura  could  be  assigned. 

On  Sheep  Creek  a  basal  limestone  yielded  Camptonectes  bel- 
listriatus; Myoplwria  lineata;  Gryphea  calceola ;  Pentacrintis  asteri- 
cus; Belemnites  densus;  and  sj^ecimens  of  Ostrea,  Trigonia,  and 
Volsella. 

•  Kino  :  Geology  of  the  40th  parallel,  Vol.  I,  p.  290. 

»  White  :  Geology  of  Northwest  Colorado,  U.  S.  Geol,  Surv.,  Vol.  XII,  1878. 


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252 


;r.  A'.  LOCHIA' 


\ 


THE    SOUTHERN    UINTA    AREA  , 

Ashley  Crcck.^ — The  thickness  of  the  Jurassic  beds  on  Ashley 
Creek  is  estimated  to  be  about  750  feet.  Of  this  thickness  50  feet 
are  blue  and  drab  colored  shales  and  limestones  carrying  Gryphea 
calceold,  Pseudomouotis  [Euiiticrotis)  citrta  and  Biicmnites  densus. 
This  stratum  corresponds  to  the  more  densely  fossiliferous  zone 
of  other  localities.  As  the  vertical  range  of  the  fossils  is  not 
given  it  is  difficult  to  say  whether  all  of  the  750  feet  should  be 
included  in  the  Jura. 

Near  Peoria  on  the  western  end  of  the  range  a  basal  lime- 
stone contains  Pseudomouotis  curta  and  is  followed  by  a  group  of 
shales  and  marls.     No  thicknesses  are  given  for  this  area. 

Wasatch  Range.' — In  Weber  canyon  of  the  Wasatch  Range  the 
Jurassic  is  estimated  to  have  a  total  thickness  of  1600  feet.  The 
lower  part  which  consists  of  vellow  and  bluish  limestones  and 
calcareous  shales  has  a  thickness  of  600  feet.  It  contains  the 
following  fossils :  Cucnllaea  haguei;  Pleuromya  stibcompressa ; 
Myophoria  lineata;  Myophoria  sp.  and  Volsella  scalpra.  As  the 
upper  1000  feet  of  arenaceous  texture  is  unfossiliferous  it  is 
more  than  probable  that  it  is  not  of  Jurassic  age.  As  the  ver- 
tical range  of  the  fossils  is  not  given  we  have  no  means  of  ascer- 
taining how  much  of  the  600  feet  may,  also,  belong  to  another 
period. 

At  the  mouth  of  Thistle  Creek  in  Spanish  Fork  Canyon  the 
following  fossils  were  found :  Lyosoma  pouelli,  Camptonectes 
stygius  and  Pitina  sp. 

THE   SOUTHERN    UTAH    AREA 

According  to  Button  3  the  known  Jura  of  Southern  Utah  has  a 
thickness  of  from  200  to  400  feet.  The  formation  consists  of  a 
series  of  calcareous  and  gypsiferous  shales.  The  beds  are  dis- 
tinctly fossiliferous  and  thin  out  toward  the  south,  entirely  dis- 
appearing in  northern  New  Mexico  and  Arizona.  A  few  fossils 
have  been  collected  from  a  number  of  localities  in  the  region. 

■  King  :  Geology  of  the  40th  Parallel,  Vol.  I,  p.  292. 

»KiNG  :  1.  c.  p,  293.  3  Geology  of  the  High  Plateaus,  Utah,  p.  150. 


mmmmmtm 


EPICONTINENTAL  SEA   OF  JURASSIC  AGE 


253 


From  specimens  collected  on  the  Santa  Clara  River  two  miles 
below  Gunlock  White  determined  the  following  si)ecies  :  Peiita- 
crinus astcricus  M.  &  H.;  and  Trigonia  sp.  Wh.;  from  near  Kanara  : 
Pentacnnus  astenciis  M.  Si.  H.;  CamptoHcctcs  stygius'^h'xic;  QnHp- 
toiieck's  bellistriotus  M.  &  H.;  from  the  northern  part  of  ac|uariiis 
plateau;  Camptoiicctes  platcssiformis  White;  Trigonia  montaiiacusis 
Meek  and  Gennllia  sp.  White ;  from  Potato  Valley,  Diamond 
Valley,  and  near  Gunnison:  Pentacrimis  asteriais  M.  &  H. 

From  the  geographic  distribution  of  the  Jura  in  this  region 
it  appears  that  the  Jurassic  sea  did  not  extend  far  south  of  the 
southern  boundary  of  Utah.  It  may  be  assumed  also  that  its 
eastern  as  well  as  its  western  shore  lines  did  not  extend  in  this 
region  much  beyond  the  state  boundaries.  From  this  point  the 
eastern  shore  line  extends  farther  and  farther  east  crossing  the 
northwest  corner  of  Colorado  thence  continuing  toward  the 
northeast  and  including  the  Black  Hills  area. 

The  thinning  out  of  the  beds  toward  the  south  may  be  due 
to  the  presence  of  a  low  land  area  at  the  south  during  this  epoch. 
A  high  land  area  should  give  a  thick  shore  deposit  of  a  coarse, 
clastic  nature.  According  to  the  above  statements,  however, 
the  beds  consist  of  calcareous  and  gypsiferous  shales  which 
indicate  either  a  somewhat  remote  shoreline  or  a  low  bordering 
land  area. 

THE    BLACK    HILLS   AREA' 

The  Jurassic  formation  forms  one  of  the  members  in  the  rim 
of  sedimentary  rocks  which  encircles  the  crystalline  area  of  the 
Black  Hills.  Here  as  in  the  central  and  southern  areas  the  Jura 
rests  upon  the  Red  beds  and  is  overlain  by  the  Lower  Cretaceous, 
the  Como  beds.  Its  thickness  is  in  the  neighborhood  of  200 
feet.  It  exhibits  in  general  about  the  same  lithological  characters 
that  are  noticeable  in  the  formation  in  the  Southern  Wyoming 
area.  The  beds  consist  of  sandstones,  arenaceous  shales  and 
marls,  and  thin  beds  of  impure  fissile  limestone. 

Whitfield'  has  determined  the  following  species  from  this 

'Jenney  :  Nineteenth  Ann.  Re;'.  U.  S.  Geol.  Surv.,  p.  593. 

'  Geology  of  the  Black  Kiii»,  '884. 


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254 


IV.  N.  LOGAN 


area:  Asterias  dtibium  Whitf.;  Pentacrinns  astcricus  M.  &  H.;  Lin- 
gtila  brevirostns  M.  &  \\.\  Rliynchonellti  myrina  M.  &  II.;  Ostrea 
stngilecnla  White;  Gryp/ica  calceola,  var.  nebrascensis  M.  &  H.; 
Pecteii  ueivbenji  VVIiitf.;  Camptonectes  bellistriaUis  M.;  Campto- 
nectes  extenuatus  M.  &  H.;  Pscudomoiwtis  cnrta  Mall  ;  Pscudomono- 
tis  orbiculata  Whitf.;  Avicula  {Oxyfonui)  mucronata  M.  &  H.; 
Gervillia  recta  M.;  Grammatodon  inornatus  M.  &  H.;  Mytilus 
wkitei  Whitf.;  Vohella  {Modiolo)  fortnosa  M.  &  H.;  Vohella  pcr- 
temus  M.  &  H.;  Astarte  fragilis  M.  &  H.;  Trapezium  belle- 
fourchensis  Whitf.;  Trapesium  subequalis  Whitf.;  Pleuromya 
newtoni  Whitf.;  Tancredia  itiornata  M.  &  H.;  Tancredia  corbuli- 
formis  Whitf.;  Tancredia  bulbosa  Whitf.;  Tancredia postica  Whitf.; 
Tancredia  zvarrenana  M.  &  H.;  Dosina  jiirassica  Whitf.;  Psammo- 
biaf  prematura  Whitf.;  Thracia?  sublevis  M.  &  H.;  Neaera 
longirostra  Whitf.;  Saxicava  jurassica  Whitf.;  Quenstedioceras 
[Cardioceras)  cordiforme  M,  &  H.;  and  Bclemnites  densus  M.  &  H, 

In  the  Big  Horn  Basin  region  Eldridge'  discusses  the  Jura 
as  follows:  "This,  so  far  as  the  evidence  obtained  indicates,  is, 
within  the  region  under  examination,  wholly  of  marine  origin. 
The  thickness  is  between  400  and  600  feet,  which  is  approximately 
maintained  over  the  entire  area  of  exposure.  Shales  constitute 
the  mass  of  the  formation  in  which  from  base  to  summit  occur 
thin  beds  of  sandstone  and  fossiliferous  limestone  of  types  char- 
acteristic of  the  Jura  in  the  Rocky  Mountain  region.  Gray  is  the 
predominating  color  of  the  shales,  but  throughout  the  formation 
red,  purple,  yellow,  slate,  and  pink,  in  greater  or  less  intensity, 
may  be  observed.  At  a  number  of  localities  a  considerable 
amount  of  siliceous  matter  appears,  in  occurrence  suggesting  the 
action  of  hot  waters. 

"The  sandstones  are  of  slight  importance.  They  are  chiefly 
gray  with  a  slight  greenish  tint.  The  lower  beds,  however,  are 
red,  shaly  and  transitional  from  the  Trias,  while  near  the  sum- 
mit are  two  of  greater  thickness,  which,  but  for  their  tint  and 
the  overlying  typical  Jura  shales,  might  be  confounded  with  the 
Dakota. 

»  Bull.  U.  S.  Geol.  Surv.  No.  119. 


iwaa:«E««>w«Bs*aM^-i>**Wiwai«wrt!ii»!w«^^ 


.j#i^.i£» 


EPICONTINENTAL  SEA  OF  JURASSIC  AGE 


255 


"The  limestones  are  nearly  all  fossiliferous,  and  of  the  drab 
color  peculiar  to  the  Jura  in  the  west.  In  thickness  they  vary 
from  a  few  inches  to  15  feet.  Three  or  four  in  the  lower  100 
feet  and  one  or  two  in  the  upper  third  of  the  formation  are  espe- 
cially prominent." 

The  formation  is  said  to  be  overlain  by  the  Dakota  sand- 
stone. If  this  so-called  Dakota  sandstone  is  at  the  same  hori- 
zon that  it  is  in  the  Freeze-Out  Hills,  and  it  seems  from  the 
description  very  probable  that  it  is,  then  the  Jura  so-called 
must  include  the  Como  beds.  The  description  of  the  upper 
part  of  the  formation  fits  the  Como,  while  the  lower  part  with  its 
fossiliferous  limestones  is  very  characteristic  of  the  Jura  both 
north  and  south  of  this  area.  The  Como  or  its  stratigraphic 
equivalent  is  recognized  both  north  and  south  of  this  region  and 
there  appears  no  good  reason  for  its  absence  in  this  area. 

THE    MONTANA    AREA 

Castle  Momttain.^ — The  Jurassic  formation  in  this  area  is  less 
than  one  half  the  average  thickness  for  the  interior.  Its  maxi- 
mum thickness  is  only  ninety  feet.  The  formation  consists  of  a 
basal  sandstone  overlain  by  a  dense  white  limestone.  The  lime- 
stone layer  is  highly  fossiliferous  and  contains  the  following 
well-known  Jurassic  forms:  Astarte  packardi ;  Trigonia  montanaen- 
sis;  Pitpui  kingi;  Pholadomya  kingi;  Ostrea  sp.;  Camptonectes 
extemiatus ;  and  Gervillia  niontanaensis. 

The  Jura  of  this  locality  rests  upon  upon  the  Carboniferous 
and  the  Red  Beds  are  not  represented.  It  is  the  belief  of  the 
writers  that  the  beds  are  wanting  altogether  in  Montana,  or  at 
least  but  sparingly  represented. 

Little  Rocky  Mountains' — The  total  thickness  of  the  Jura  for 
this  region  is  placed  at  1 00  feet.  The  beds  consist  of  shaly 
gray  limestones  which  change  to  impure,  marly  shales  and  argil- 
laceous limestones.  They  rest  on  limestones  of  Carboniferous 
age  and  the  Red  Beds  are  again  absent. 

'Weed  and  Pirsson,  Bull.  139,  U.  S.  Geol.  Surv.,  1896. 
"Weed  and  Pirsson,  Jour.  Geol.,  Vol.  IV,  1896. 


•VT&t^i?SXJ^'*4«5 


-»SS»re** 


l\ 


I 


256 


H^.  A.  LOGAN 


i 


The  Jiii-issic  limestones  contain  the  following  species:  Astarti 
meeki;  Bilemnites  densiis;  Plcuromya  iubcompressa ;  Gryphca  cal- 
ccola,  var.  nebrasccnsis ;  and  a  fragment  of  an  undetermined 
Ammonite. 

This  is  one  of  the  most  northerly  areas  from  which  Jura  has 
been  recorded  for  Montana.  If  the  formation  is  present  in 
the  Hear  I'aw  Mountains  which  lie  to  the  northwest  of  this  area 
it  has  not  been  differentiated. 

Three  Forks} — The  Jura  has  a  thickness  in  this  area  of  from 
300  to  400  feet.  The  lower  beds  rest  on  a  basal  (juartzite  and 
consist  of  argillaceous  limestones  which  carry  characteristic 
Jurassic  fossils  The  middle  and  upper  beds  are  more  arena- 
ceous than  the  lower  beds  and  are  non-fossiliferous.  Under 
such  conditions  it  is  very  questionable  whether  they  should  be 
assigned  to  the  Jura.  It  is  very  probable  that  the  thickness  of 
the  Jura  in  this  area  conforms  more  nearly  to  that  assigned  to  it 
in  other  areas  of  Montana. 

Livingston." — The  Jurassic  formation  of  the  Livingston  area 
has  a  thickness  estimated  at  400  feet.  It  consists  at  the  base  of 
a  massive,  cross-bedded,  ripple-marked  sandstone.  This  sand- 
stone is  overlain  by  a  layer  of  impure  fossiliferous  limestone 
containing  Plcuromya  subcompressa  M.  The  limestone  is  fol- 
lowed by  a  bed  of  arenaceous  limestones  containing  shell  frag- 
ments. Since  the  lower  layer  is  non-fossiliferous  it  may  or  may 
not  represent  a  part  of  the  Jura,  but  there  is  the  possibility  of 
an  overestimation  of  thickness   here  as  well   as  in  the  Three 

Forks  area. 

Although  the  thicknesses  given  tor  the  Three  Forks  and 
Livingston  area  are  not  extremely  large,  yet  they  are  nearly 
double  that  given  for  the  other  Montana  areas.  But  as  has  been 
pointed  out,  this  lack  of  harmony  may  be  due  to  the  inclusion 
of  beds  belonging  to  other  formations.  If  the  faunal  relations 
are  not  carefully  worked  out  in  connection  with  the  stratigraphy 
errors  are  likely  to  occur  either  in  the  direction  of  the  overlying 

«  Peai.e,  U.  S.  Geol.  Surv.,  Three  Forks  Folio,  1896. 

"IDUINGS  and  Weed,  U.  S.  Geol.  Surv.,  Livingston  Folio,  1894. 


ii 


i 


If 


■4. 


'  ^'ittriiaariiiiiioii 'ir    ■"■i-^-f""'"'"^"'^ 


wmmmm 


'^m^' 


I 


If 


EPICONTINENTAL  SEA  OF  JUKASS/C  AGE 


-     t  , 
257 


or  the  underlying  beds.  For  the  Jura  in  many  localities,  so  far 
as  physical  characters  are  concerned,  grades  almost  inipercep- 
tively  into  the  Red  Beds  below  anil  the  Como  above. 

Judith  Mounttiins.^ — Weed  and  I'irsson  give  the  following 
section  as  representing  the  Jura  in  the  Judith  Mountains. 
The  base  is  separated  from  the  Carboniferous  by  a  sheet  of 
porphyry. 


FMt. 

10 


5 


13 

25 


>s 


5 


8 


1.  Limestone,  dark  gray,  lamiiiated,  and  shaly         .... 

2.  Limestone,  blue  to  gray    in   color,  hard   in  texture,    and   carrying 
Ostre;e  in  3  to  5-foot  beds,  sejjarated  by  thinner  platy  beds 

3.  No  exposure       -         •         ........ 

4.  Shaly,  argillaceous,  impure  limestone,  dove  colored,  weathering  buff 
on  joint  faces  and  of  typical  Jurassic  aspect  ... 
Shaly  beds,  seldom  exposed,  carrying  oolitic  limestone.     Green  or 
sandy  limestone  of  drab  color              ...... 

Rough  weathering  limestone,  fine  grained,  cross-bedded  and  fissile, 
carrying  fossils        ......... 

Sandy  limestone  like  that  above,  but  irregularly  bedded  and  resem- 
bling sandstone ;  granular  and  saccharoidal  in  texture,  carries  shell 
fragments  .......... 

Irri-trularly    platy,    earthy-brown,    gray    limestone    carrying    shell 
remains  of  Gryphea  and   Ostrea,    weathering   dark    brown,   rarely 

granular 

Marly  shales  and  limestone,  dove  colored,  carrying  fossils  noted  in 
following  pageu,  seldom  exposed,  Gryphea  most  abundant  here  - 
No  exposure,  but  debris  of  sandstone  ..... 
Ellis  sandstone,  variable,  buff,  platy  sand  rock;  pink  blotched  at  base 
with  occasional  shells ;  cross-bedded  purple-brown  outcrop.  It  is 
at  the  top  a  limestone  full  of  black  and  white  quartz  sand  grains 
and  forms  a  dark  brown  ridge     -..---. 

This  section  gives  the  total  thickness  of  the  Jura  for  this 
region  at  184  teei,  which  is  nearly  double  that  of  the  Little 
Rocky  and  Castle  Mountain  areas. 

The  fossils  collected  from  the  horizotil  mentioned  above  are  : 
Ostrea  strigilecula  White;  Gryphea  calceola  var.  nebrascensis  M.  & 
H.;  Modiola  subimbricata  M.;  Cucullaea  haguei  M..\  Pleuromya  sub- 
compressa  M. 

'  Weed  and  Pirsson,  Eighteenth  Ann.  Rept.,  U.  S.  Geol.  Surv.,  Ill,  p.  445. 


10 
II 


30 
60 


12 


..^^ 


358 


ir.  N.  LOGAN 


Ytlhxvstone Piirk.^ — The  tiiickncs.s  of  the  formation  for  this  area 
is  placed  at  300  feet.  It  consists  of  sandstones,  marls,  limestones, 
and  days,  and  contains,  aciordinjr  to  Stanton,' the  following  spe- 
cies :  Pcntncrinus  nskruus  M.  &  II.;  Rliynihonilln  tnyrina  Hall  Cfe 
VVliitf.;  RyiK/tontUii  f:^n<itliof>lt<>rti  M.;  Ostna  .slfij<;iliinlii  White; 
Ostna I'/igiltntiHt  M . ;  (iryphea plonoconvexn  Wh i t f . ;  (iryplicn  calccola 
var.  ucbrasicnsis  M.  &  H,;  Lima  cinnahiinnsis  Stan.;  Ciimptomctes 
hclHstriiitus  M.;  CamptomctcshellistntUus  var.  ^/mA///.v  Stanton  ;  Ciimp- 
toiiectcs  pirtenuiitriatus  Hall  it  VVhitf.;  Cmnptoiiictes  plntessiformis 
White;  Avicula  {Oxytomti)  Wyomiiij^^einis  .Stan.;  PscmiomonoHs 
Ctirta  (Hall)?;  Gervillia  mo  nUi  mien  sis  M.;  GcrviHia  sp.  Stan.; 
Mcdiolii  suhimbricata  Meek;  Pinna  kin^i  M.;  CmiiUaca  hagnei  M.; 
Tr'gonia  americana  M.;  Tngonia  i/egan/issima  M.;  Trigonia  mon- 
tanaensis  M.;  Astarte  mecki  Stan,;  Astartc  s|).  Stanton  ;  Tancredia? 
knoivUoni  Stun.;  Protocaniia  slinmardi  M.  &  H.;  Cyprinaf  Cinna- 
biiiriisis  Stanton  ;  CypHna?  iddinirsi  Stanton  ;  Cypricardia?  haguei 
Stanton;  Pholadomya  kingi  M.;  Pholadomya  inaeqiiiplicata  Stan.; 
Homomya  gatlatinensis  SiAn.\  Plenromya  siibcompnssa  M.\  Thracia 
UHcdi  Stanton;  Thracia?  montanacnsis  (Meek)?;  Anatina  {Cfr- 
comya)  punctata  Stan.;  Anatina  [Cercomya)  sp.  Stan.;  Neritina 
wyomingcnsis  Stan.;  Lyosoma  powelli  White;  Turitella  sp.  Stan.; 
Natica  sp.  Stan.;  Oppeliaf  sp.  Stan.;  Perispinctes  sp.  Stan.;  and 
Belemnitcs  dcnsus  Meek  and  Hayden. 

THE    CANADIAN    AREA 

In  the  Queen  Charlotte  Islands  Whiteaves^  noted  the  occur- 
rence of  the  following  species,  which  are  common  to  the  Jura  of 
the  Interior:  Plenromya subcompressa  Mk.;  Astarte packardi^Wxie; 
Avicula  {Oxytoma)  mucronata  Mk.;  Gryphea  calccola  var.  nebras- 
censis  M.  &  H.;  Lyosoma  powelli  V\/hite  ;  Belemnites  densus  M.  &  H.; 
Belemnites  skidgatensis  Whiteav.;  Grammatodon  itwmatus  Whiteav.; 
Modiola  subimbricata  Mk.;  and  Camptonectes  extenuatus  Mk. 

Although  Whiteaves  recognized  the  interior  affinity  of  these 
forms,  he  was  inclined  to  put  both  groups  into  the  Cretaceous 

»U.  S.  Geol.  Surv.,  Yellowstone  Park  Folio,  1896. 

•U.  S.  Geol.  Surv.,  Yellowstone  Park  Monograph,  XXXII,  p.  601,  1899. 

'Geol.  Surv.,  Canada,  Mesozoic  Fossils,  Vol.  I. 


T 


KPICONTINENTAI.  SKA   OF  JURASSIC  AGE 


259 


T 


rather  than  tlic  Jura.  Hut  the  Jurassi'^  a^jc  of  these  beds* 
is  now  sufficiently*  well  established  not  to  rVjuire  further  tlis- 
cussion. 

Not  only  is  this  fauna  rc|)rcsv'ntcd  in  (he  islands  ju*t  men- 
tioned, but  it  occurs  also  on  the  coiui  irnt  at  souie  ronsiderable 
distance  inland.  From  fossils  collected  bs  Vi  M,  Dawson  oti  the 
Iltasyouco  River  in  Hritish  Columbia  about  Parallel  53"  and 
Lonjjfitude  126"  West,  VVhiteaves'  recognized  the  following  spe- 
cies; PU'uromyn  suf)iomf>r(ss<i  ^\i.\  Pleuroniyii  licvigiitd  Whiic^LV,', 
AsUirte packordi  White;  Trigonui  ihnvsoni  Whiteav.;  Moiiiola  for- 
tuosd  M.  &  H.;  Girvilleo  monUntaensii  Mk.;  (hyphen  cnlceola  var. 
nchrnscensis  M.  &  II.;  GromnuUodon  inormUiis  Whiteav.;  Oleoste- 
phanus  loganianus  Whiteav. 

These  fossils  were  found  in  the  felsites  and  porphyrites  of 
the  metamorphic  rocks  lying  cast  of  the  Coast  Range.  They 
contain  species  common  to  both  the  Queen  Charlotte  and  the 
Interior  faunas. 

From  fossils  collected  by  G.  M.  Dawson  at  Nicola  Lake  in 
British  Columbia  Hyatt'  determined  the  Jurassic  age  of  certain 
beds  in  that  region  lying  above  the  Triassic.  The  fossils  col- 
lected are  :  Rhynchonella  gnathophoriat ;  Pecten  acntiplicatus  Gabb  ; 
Entolium  sp.  Hyatt;  Limaparva  Hyatt. 

Just  north  of  Parallel  51°,  near  the  east  end  of  Devil's  Lake, 
which  is  situated  on  the  eastern  border  of  the  Front  Range  of 
the  Rockies,  McConnelM  found  an  outlier  of  Jurassic  which 
contained  the  following  fossils:  Avicula  (Oxytonia)  mucronata; 
Trigonia  intermedia ;  Trigonarca  ttimida;  Terebratula,  Osina,  Camp- 
tonectes,  Linui,  Cyprina,  Ammonites,  and  Belemnitcs.  This  locality 
serves  as  a  connecting  link  between  the  Montana  area  and  the 
localities  to  the  west,  as  it  is  situated  midway  between  the  two. 
The  above-named  group  of  fossils  contains  one  species  and  a 
number  of  genera  common  to  the  Interior  and  the  Pacific  Coast 
deposits. 

'  Loc.  cit. 

'Kept,  of  Geol,  Surv.,  Canada,  1894,  p.  5I> 

3Rept.  of  Geol.  Surv.  Canada,  1896,  p.  I7d. 


« 

.   260 

PV.  N.  LOGAN 
THE    ALEUTIAN    AREA 

Grewingk"  was  the  first  to  announce  the  occurrence  of  beds 
of  Jurassic  age  in  Alaska.  These  beds  were  discovered  at  differ- 
ent places  along  the  Alaskan  Peninsula  and  the  Aleutian  Islands. 
From  the  distribution  of  these  beds  as  mapped  by  Grewingk  the 
Alaskan  Peninsula  and  the  Aleutian  Islands  must  have  been 
under  water  during  Jurassic  times. 

In  1872  Eichwald'  described  an  assemblage  of  fossils  col- 
lected from  these  same  beds  and  correlated  them  with  the 
Northern  Russia  beds  of  the  same  age,  but  put  both  formations 
in  the  Lower  Cretaceous.  .Some  fossils  were  collected  from  the 
same  region  by  Dall  in  1883.  These  forms  were  described  by 
White,3  who  after  making  a  study  of  them  and  comparing  them 
with  Eichwald's  descriptions,  decided  that  the  latter  was  wrong 
in  his  assignment  of  the  beds  to  the  Cretaceous.  He  found  them 
to  be  closely  allied  to  the  Jurassic  of  Northern  Russia.  One 
species,  Aucella  concentrica  Fisher,  he  considers  either  identical 
or  only  a  variety  of  the  Eurasian  Jurassic  form  of  that  name. 

Hyatt,"*  in  speaking  of  these  deposits,  says:  "The  fauna  of 
the  Black  Hills,  acknowledged  to  be  Jurassic  Ly  everyone  but 
Whiteaves,  is  in  part  apparently  synchronous  with  that  of  the 
Aleutian  Islands  and  Alaska,  as  described  by  Eichwald  and 
Grewingk." 

The  position  of  these  beds  and  the  relation  of  the  fauna  with 
the  northern  Eurasian  fauna  points  clearly  to  an  Arctic-Pacific 
connection  by  way  of  the  Bering  waters  during  this  epoch.  More- 
over we  now  have  an  almost  continuous  faunal  record  extending 
from  Alaska  to  southern  Utah. 

Conclusions. —  An  examination  of  the  above  sections  will  show 
that  the  thickness  of  the  Jura  in  the  interior  is  not  very  great. 
An  average  of  ten  localities  gives  a  thickness  of  but  little  over 

'Russian  Kaiserl.  Mineral  Gesell.,  1848-9. 

"Geognostiscli-Paleontologische  Bemerkungen  iiber  die  Halbinsel  Mangischlak 
und  die  Aleutsciien  Insel. 

3  Bull.  U.  S.  Geol.  Surv.  No.  4,  1884. 

■•  Bull.  Geol.  Soc.  Am.,  Vol.  V,  1894,  p.  409. 


» 


wnwMomKvn 


EPICONTINENTAL  SEA   OF  JURASSIC  AGE 


261 


ntical 

e. 

na  of 

e  but 

f  the 

■ 

.  and 

with 

acific 

itore- 
iding 

1 

show 

l^reat. 

'  » 

over 

schlak 

« 

■Kor:^.!!.-!! -:--,• 

.  .■;.»---*'r!i;«,jss«iW;ii^M 

« 

two  hundred  feet.  In  fourteen  localities  the  thickness  is  under 
four  hundred  feet.  These  localities  are  scattered  throughout  the 
length  and  breadth  of  the  interior  province.  In  all  the  areas  for 
which  greater  thicknesses  have  been  recorded  there  are  none  in 
which  the  entire  thickness  could,  without  question,  be  assigned 
to  the  Jura. 

The  lithological  character  of  the  beds  is  much  the  same  for 
all  areas.  The  formation  consists  everywhere  of  essentially  the 
same  group  of  arenaceous  clays,  shaly  marls,  impure  limestones 
and  sandstones.  The  order  of  succession  of  the  beds  implies 
ever  changing  conditions  of  sedimentation.  Thin  beds  of  sand- 
stone are  overlain  by  thin  beds  of  fossilferous  clays,  marls,  or 
limestones ;  and  these  in  turn  are  followed  by  another  similar 
group. 

The  absence  of  any  considerable  thickness  of  limestone  over 
a  large  area  indicates  that  for  no  great  period  of  time  were  the 
waters  of  the  sea  entirely  free  from  clastic  sediments.  The 
presence  of  cross-bedded  sandstone  and  ripple-marked  layers  at 
different  horizons,  the  almost  universal  presence  of  Ostrea  and 
other  shallow  water  forms,  together  with  the  stratigraphic  and 
iithologic  characters  just  mentioned  prove  that  the  waters  of  the 
sea  were  not  of  great  depth  ;  that  the  sea  was  not  of  the  abysmal 
type.  It  was  not  a  sea  comparable  in  depth  to  the  Mediterranean 
but  was  a  shallow  epicontinental  sea.  From  the  geographic  dis- 
tribution of  the  known  Jurassic  the  outlines  of  this  sea  were  as 
indicated  on  the  map'  accompanying  this  paper. 

From  the  character  and  extent  of  the  sea  it  may  be  assumed 
that  no  extensive  epeirogenic  movement  was  necessary  for  its 
inauguration,  providing  the  antecedent  topographic  conditions 
were  favorable.  In  the  northern  part  of  the  area  there  is  evidence 
that  a  considerable  period  of  erosion  preceded  the  Jura,  as  the 
Red  Beds  are  absent  and  the  Jura  rests  on  the  Carboniferous. 
This  period  of  erosion  may  have  been  sufficient  to  reduce  the 
land  area  to  approximate  base  level  in  which  case  a  very  slight 
warping  would  have  been  sufficient  to   let  the  waters  of  this 

'See  p.  245. 


J 


262 


IV.  N.  LOGAN 


shallow  sea  in  upon  the  continent.  A  very  slight  increase  in  the 
capacity  of  the  ocean  basin  would  suffice  to  draw  the  water  off 
the  continent  at  the  close  of  the  period.  The  increase  in  the 
capacity  of  the  ocean  may  have  been  accomplished  by  a  slight 
settling  of  the  oceanic  segment.  The  withdrawal  of  the  waters 
of  the  epicontinental  sea  was  doubtless  the  initial  step  in  the 
movement  which  ended  in  the  elevation  of  the  Sierra  Nevada 
Mountains  ;  for  the  withdrawal  took  place  at  the  close  of  the 
Oxfordian  stage  or  during  the  Corallian  and  according  to  Diller' 
the  orogenic  movement  which  produced  the  Sierra  Nevada  and 
Klamath  Mountains  took  place  at  the  close  of  the  Corallian.  If 
these  interpretations  be  logical  ones  we  may  assume  that  it 
required  little  or  no  bodily  movement  of  the  continent  to  pro- 
duced either  the  inauguration  of  the  Jurassic  sea  or  its  withdrawal 
from  the  continent.  It  may  be  asserted  further  that  there  is 
nothing  connected  with  its  history  which  is  inimical  to  the  doc- 
trine that  the  continent  had  in  general  its  present  outline  during 
Jurassic  times  and  that  the  waters  of  the  submerged  portions 
were  of  an  epicontinental  nature. 

The  writer's  study  of  the  faunal  conditions  in  the  field  has 
led  him  to  the  opinion  that  only  one  fauna  is  to  be  recognized 
in  the  Jurassic  deposits  of  the  interior  province.  A  comparison 
of  the  fossils  collected  from  the  different  areas  just  discussed 
serves  to  strengthen  the  opinion.  Everywhere  the  formation  is 
characterized  by  about  the  same  group  of  fossils,  of  which  the 
more  characteristic  ones  are:  Pentacrinus  astericus,  Belemnites 
densus,  Camptonectes  bellistriatus,  Pseudomonotis  curta  and  Cardi- 
oceras  cordifonne.     These  forms  all  existed  contemporaneously. 

Stanton"  discusses  the  view  expressed  by  Hyatt 3  that  more 

than  one  Jurassic  fauna  may  be  represented  in  the  Interior  and 

arrived  at  the  following  conclusion:  "the  stratigraphic  relations 

and  the  geographic  distribution   of  the  marine  Jurassic  of  the 

Rocky  Mountain  region  are  in  favor  of  the  idea  that  all  of  these 

deposits  were  made  contemporaneously  in  a  single  sea." 

•  Bull.  Geol.  Soc.  Am.  Vol.  IV,  p.  228. 

»  f.  S.  Geol.  Surv.  Yellowstone  Park  Monograph  XXXII,  1 899,  pp.  602-604. 

3  Bull.  Geol.  Soc.  Am.  Vol.  Ill,  1892,  pp.  409-410. 


^1 


" 


EPICONTINENTAL  SEA   OF  JURASSIC  AGE  263 

This  fauna  according  to  Hyatt  belongs  to  the  Oxfordian  stage 
of  the  Upper  Jura  or  Malm.     In  the  Taylorville  series  of  Cali- 
fornia   he    recognized    the    Callovian.    the    Oxfordian    and    the 
Corallian  stages  of  the  Upper  jura.      But  as  has  been  stated  above 
none  but  the  middle  stage  has  been  recognized  in  the  Interior. 
Relation  of  the  interior  fauna  to  the  northern  eurasian  fauna. — 
The  discovery  of  beds  of  Jurassic  age  in  the  interior  was  first 
announced  by  Meek'  in   1858.     In  correlating  these  beds  with 
the  Jura  of  the  Old  World  he  says  :  "The  organic  remains  found 
in  these  series  present,  both  individually  and  as  a  group,  very 
close  affinities  to  those  in  the  Jurassic  epoch  in  the  Old  World ; 
so  close  indeed,  that  in  some  instances,  after  the  most  careful 
comparisons  with  figures  and  descriptions,  we  are  left  in  doubt 
whether  they  should  be  regarded  as  distinct  species,  or  as  vari- 
ties  of  well-known  European  Jurassic  forms.     Among  those  so 
closely  allied  to  foreign  Jurassic  species  may  be  mentioned  an 
Ammonite  we  have  described  under  the  name  of  Ammonites  cordi- 
formis  which  we  now  regard  as  probably  identical  with  Ammonites 
cordatus  of  Sowerby ;  a  Gryphea  we  have  been  only  able  to  dis- 
tinguish  as    a   variety   from    G.   calceola   Quenstedt ;    a   Pecten, 
scarcely  distinguishable   from  Pecten  lens  Sowerby;  a  Modiola, 
very  closely  allied  to  M.  cancellata,  of  Goldfuss ;  a  Belemnite, 
agreeing  very  well  with  B.  excentricus." 

Since  the  publication  of  the  above  statements  by  Meek  the 
paleontology  of  the  European  Jura  has  been  more  completely 
worked  out  and  some  of  the  faunas,  particularly  that  of  north- 
ern Russia,  are  found  to  have  still  closer  affinities  to  the  Ameri- 
can interior  fauna.  The  Jurassic  faunas  of  America  have  also 
received  many  additions  at  the  hands  of  the  American  paleon- 
tologists Gabb,  Hyatt,  Meek,  Smith,  Stanton,  White,  Whiteaves, 
and  Whitfield.  All  of  these  studies  have  tended  to  strengthen 
the  opinion  just  expressed. 

The  following  comparison  of  forms  which  are  so  closely 
allieti  as  to  deserve,  in  many  cases,  to  be  called  varieties  of  the 
same  species  will  serve  to  show  the  close  affinity  of  the  interior 

•Geological  Report  of  the  Exploration  of  the  Yellowstone  and  Missouri  Rivers. 


IT 


264 


IV.  N.  LOGAN 


American  tauna  to  the  fauna  of  northern  Eurasia :  Belcmmtes 
pamicramis  d'Orb.  and  Belemnitcs  densiis  Mk.;  Astartc  dubomanus 
d'Orb.  and  Astarte  pnkardi  White;  Avicula  volgcnsis  d'O.  and 
Avicula  mucromta  Mk.;  Pcntacrinm  scalans  Goldf.  and  Penta- 
crinus  astericus  M.  &  H.;  Goniomya  dubois  d'Orb.  and  Gomoniya 
montanaensis  Mk.;  Gryphea  calceola,  Quen.  and  Gryphea  caceola 
var.  nebmsccnsis  Mk.;  Cardioceras  cordattis  Sow.  and  ^/'^w^^mi 
cordiforme  Mk.  The  faunas  taken  as  a  whole  exhibit  the  close 
relationship  in  a  much  more  forcible  manner  than  the  comparison 

of  a  few  species. 

This  northern  Eurasian,  or  Cardioceras  fauna  is  thought  to 
have  had  its  origin  on  the  northern  shores  of  the  Eurasian  con- 
tinent, and  to  have  migrated  from  there  to  American  waters. 
This  assumption  is  based  on  the  sudden  appearance  of  the 
fauna  in  America  and  its  close  affinities  with  older  Eurasian 
faunas.  The  present  geographic  distribution  of  the  fauna 
indicates  a  northern  connection. 

A  later  Jurassic  fauna,  the  Ancella  fauna,  probably  had  its 
origin  in  the  north  and  migrated  to  Pacific  waters.  This  fauna, 
however,  did  not  reach  the  interior  province  of  America  as  the 
waters  of  the  epicontinental  sea  had  been  withdrawn  before  its 
appearance.  This  later  migration  extended  along  the  Pacific 
coast  as  far  south  as  Mexico. 

Both  of  the  faunas  just  mentioned  belong  to  the  Upper  Jura, 
but  the  Lias  and  Middle  Jura  are  also  represented  in  the  Cali- 
fornian  province.  The  Upper  Jura,  however,  represents  the 
maximum  encroachment  of  the  ocean  on  the  American  con- 
tinent as  well  as  on  the  Eurasian  continent.  It  also  marks  the 
maximum  expansion  of  marine  life,  induced  doubtless  by 
increased  feeding  grounds. 

Connection  of  the  sea  with  the  ocean.— The  question  as  to  where 
the  interior  sea  had  its  connection,  or  connections,  with  the 
ocean  is  important  in  estimating  the  extent  of  the  submergence. 
That  the  sea  had  a  Pacific  Ocean  connection  there  seems  no 
longer  room  for  doubt.  The  occurrence  in  the  Queen  Charlotte 
fauna  of  so  many  species  common  to  the  interior  places  the 


EPICONTINENTAL  SEA  OF  JURASSIC  AGE  26$       , 

question   beyond   controversy.     That  there  was  communication 
between  the  Arctic  and  the  Pacific  is  supported  by  the  presence 
of  Arctic  species  in  the  Pacific  fauna.     From  the  distribution  of 
the  Jurassic  sediments  as  given  in  the  preceding  pages  it  may  be 
asserted  with   a  measurable  degree  of  confidence  that  the   con- 
nection between  these  two  bodies  of  water  was  during  Jurassic 
times  as  it  is  today  by  way  of  the  Bering  waters.     As  the  pres- 
ence of   Jurassic  deposits   on    the   Alaskan    Peninsula    and  the 
Aleutian   Islands  testify  to  the  submergence  of  those  areas,  it 
may  be  assumed  that  communication   between  the  two  oceans 
was  somewhat  freer  than  at  present. 

The  question  which  is  now  brought  to  mind  is  whether  the 
interior  sea  had  any  other  connection  with  the  ocean.  The 
character  of  the  fauna  excludes  any  hypothesis  favoring  a 
southern  connection  either  with  the  Gulf  of  Mexico  or  the 
Pacific  If  there  had  been  such  a  connection  a  southern  facies 
would  be  expressed  in  its  fauna.  Such  evidence  is  entirely 
absent  The  evidence  against  any  other  Arctic  connection  is 
largely  negative,  but  as  such  is  measurably  strong.  The  inves- 
tigations of  American  and  Canadian  geologists  have  failed  to 
bring  to  light  any  Jurassic  deposits  in  the  North  aside  from 
those  already  described,  although  approximately  the  whole  area 
where  we  should  expect  to  find  them  has  been  gone  over. 

McConnell,'  who  made  geological  investigations  in  Athabasca 
and  along  the  Finlay  and  Porcupine  Rivers,  found  Cretaceous 
beds  resting  on  Devonian  and  Carboniferous  strata.  The  interval 
of  time  which  elapsed  between  the  Carboniferous  and  the  Lower 
Cretaceous  is  not  represented  in  this  region. 

Spurr'  found  the  same  conditions  to  obtain  for  the  Upper 
Yukon  region  of  Alaska  and  the  neighboring  British  territory. 
The  Lower  Cretaceous  rests  on  Devonian  or  Carboniferous  rocks. 
As  before  stated  this  evidence  is  merely  negative.  Jurassic 
rocks  may  have  been  deposited  and  afterwards  cut  away.     But, 

'  Geol.  Survey  of  Canada,  Vols.  V  and  Vll. 

»Geol.  of  the  Yukon  Gold  District,  U.  S.  Geol.  Surv.,  Seventeenth  Ann.  Rept., 

1897- 


266 


IV.  N.  LOGAN 


in  that  case,  we  should  expect  to  find  remnants  of  the  former 
beds  unless  it  be  assumed  that  a  long  interval  of  time  preceded 
the  deposition  of  the  Lower  Cretaceous.  Paleontologic  and 
stratigraphic  evidence  is  not  in  harmony  with  this  assumption. 
The  Lower  Cretaceous  beds  of  California  which  are  but  slightly 
unconformable  with  the  Upper  Jurassic,  having  a  closely  related 
fauna,  are  correlated  with  the  Lower  Cretaceous  of  the  region 
under  discussion.' 

In  many  places  in  the  interior  region  the  Lower  Cretaceous 
rests  conformably  on  the  Jurassic.  This  fact  has  been  fully 
brought  out  in  the  preceding  pages.  It  cannot  be  affirmed  that 
the  interior  sea  first  had  its  connection  with  the  Arctic  and  then 
gradually  spread  its  waters  farther  and  farther  west  until  it  united 
with  the  Pacific.  For  if  this  were  true  we  should  find  in  the 
interior  first  a  fauna  composed  wholly  of  northern  species,  fol- 
lowed later  by  a  fauna  containing  both  Arctic  and  Pacific  types. 
But  no  such  conditions  find  expression  in  the  faunal  relations  of 
the  interior.     Only  one  fauna  exists  in  the  interior. 

There  exists  at  present  no  evidence  which  will  support  the 
view  held  by  Neumayr,'  that  the  whole  of  Alaska  and  all  of  that 
portion  of  British  America  lying  north  of  the  interior  Jurassic 
area  of  the  United  States  was  submerged  during  this  epoch.  All 
that  can  be  asserted  positively  is  that  the  Aleutian  Islands  and 
Alaskan  Peninsula,  in  part  at  least,  a  narrow  margin  along  the 
Alaskan  coast  and  a  wider  area  in  California  and  Mexico  was 
under  water,  while  an  arm  of  the  Pacific  extended  in  upon  the 
continent  from  the  region  of  the  Queen  Charlotte  Islands.^ 

Lack  of  communication  between  the  provinces. — The  Jura  of  Cal- 
ifornia and  Nevada  contains  a  fauna  which  is  very  different  from 
that  of  the  interior,  although  the  faunas  are  contemporaneous. 
To  explain  the  difference  between  the  two  faunas  Neumayr 
assumed  that  that  they  belonged  to  two  distinct  climatic  prov- 
inces.    He  assumed  that  the  interior  fauna  was  a  Boreal  fauna 

"Spurr,  1.  c.,  p.  183. 

•See  map  p.  «67..  copied  from  Erdgeschichte,  p.  336. 
s  See  map  p.  245. 


k 


■irfihM'iftiai  m  i  rtiiiwmiiif^T. 


hPICONTlNES'TAL  SEA   OF  J  UN  ASS /C  AGE 


167 


268 


IV.  A.  LOG  A  A 


which  lived  in  an  arm  of  the  Arctic  Ocean,  and  that  the  Cal- 
ifornian  fauna  belonged  to  another  climatic  province,  the  north 
temperate. 

In  a  recent  discussion  of  the  subject  Ortman '  has  shown 
very  conclusively  that  the  faunal  differences  of  Jurassic  times, 
so  far  as  the  Eurasian  continent  is  concerned,  were  not  due  to 
climatic  zones.  The  distribution  of  the  interior  or  Cardioceras 
fauna  favors  this  view  for  the  North  American  continent.  The 
Cardioceras  fauna  is  found  distributed  through  a  range  of  lati- 
tude extending  from  37°  to  80°  north.  Its  southernmost  exten- 
sion is  not  as  placed  by  Neumayr  in  the  neighborhood  of  46°, 
but  is  at  least  as  far  south  as  37°,  and  is  found  in  approximately 
the  same  latitude  as  the  Californian  province.  Moreover,  the 
later  (for  the  American  region)  Jurassic  fauna,  the  Aucella,  has 
been  reported  from  Mexico."  The  Aucella  fauna  also  had  its 
origin  in  northern  Eurasian  waters.  Its  geographic  range  was 
from  80°  north  to  25°  north.  This  means  an  extension  of  Neu- 
mayr's  Boreal  province  to  within  25°  degrees  of  the  equator ! 
The  great  geographical  range  of  this  fauna  indicates  that  there 
was  little  or  no  climatic  restriction  to  its  migration.  In  so  far 
as  the  evidence  can  be  deduced  from  the  geographic  distribu- 
tion of  the  American  Jurassic  faunas  the  climate  of  the  period 
may  be  said  to  have  been  more  uniform  than  it  is  today. 

The  above  facts  are  perhaps  sufficient  to  show  the  weakness 
of  the  climatic-zone  hypothesis.  It  now  remairs  to  suggest  an 
alternative  line  of  investigation.  In  seeking  for  the  causes  for 
the  want  of  communication  between  the  provinces  it  may  be 
possible  to  draw  some  analogy  from  the  faunal  and  topographic 
conditions  as  they  exist  today  on  the  Pacific  coast.  There  are 
at  present  on  the  Pacific  coast,  according  to  Fischer,^  two 
faunal  provinces,  the  Aleutian,  corresponding  in  position  to  the 
Queen  Charlotte  of  Jurassic  times,  and  the  Californian,  corres- 
ponding to  the  Jurassic   province  of  the  same  name.     The  line 

•  Am.  Jour.  Sci.  Vol.  I,  1896,  p.  257. 

"Nitikin,  Neus  Jahrb.  Min.  Geol.  Pal.,  1890,  II,  p.  273. 

3  Manuel  ConcholoKie. 


\ 


EPICONTINENTAL  SEA   OF  JURASSIC  AGE 


269 


separating  these  two  provinces  is  placed  in  the  vicinity  of  Van- 
couver Island.  The  faunal  interrelations  of  these  two  provinces 
are  as  follows:  Of  seventy-eight  genera  occurring  in  the  two 
provinces  nine  are  common  to  both  ;  of  one  hundred  and  four 
species  six  are  common  to  both  ;  and  of  ten  circunipolar  species 
which  have  reached  Vancouver  Island  and  Puget  Sound  only 
four  occur  in  California,  and  but  one  in  Lower  California. 
From  these  conditions  it  will  be  seen  that  communication 
between  the  two  provinces  is  almost,  if  not  quite,  as  thoroughly 
prohibited  now  as  it  was  during  Jurassic  times.  The  question 
which  now  arises  is  what  restricts  communication  between  the  two 
provinces  at  present  ?  It  cannot  be  said  to  be  due  to  climate 
alone,  for  why  in  that  case  should  the  circumpolar  species  be 
found  so  far  south  ?  And  why  should  they  all  be  found  in  Puget 
Sound  and  not  be  found  farther  south  ?  This  seems  to  be  an 
exception  to  the  general  rule  that  the  climatic  provinces  of  the 
present  time  are  connected  by  transition  zones.  For  the  line  of 
demarcation  is  moderately  sharp. 

Aside  from  the  matter  of  climate  there  are  two  physio- 
graphic conditions  which  may  be  operative.  The  first  of  these 
lies  in  the  extreme  narrowness  of  the  sumerged  shelf  lying  to 
the  north  and  west  of  Puget  Sound.  This  shelf  teeming  with 
organisms  already  well  established  offers  small  inducement  to 
migratory  forms.  And  only  the  more  hardy  forms  would  be 
likely  to  survive  the  struggle  for  existence  under  such  circum- 
stances as  are  here  postulated.  Thus  the  change  of  species 
from  one  province  to  the  other  is  necessarily  slow. 

There  are  good  reasons  for  believing  that  throughout  the 
Mesozoic  era  these  topographic  conditions  of  the  Puget  Sound 
region  were  much  as  they  are  at  present.  During  the  Horse- 
town  epoch  the  Pacific  shoreline,  although  it  lay  a  considerable 
distance  east  of  the  present  shoreline  in  California  and  Oregon, 
very  closely  approximated  it  in  the  Puget  Sound  area.  The 
Chico  also  had  a  very  restricted  epicontinental  area  at  that 
point  as  the  Chico  shoreline  extended  only  to  the  eastern  coast 
of  Puget  Sound.    In  California  and  Oregon,  however,  its  eastward 


ijre 


IV.  N.  LOGAN 


% 


extension  was  far  beyond  that  of  the  Horsetown.'  The  Jurassic 
beds  do  not  occur  in  the  Fuget  Sn\uid  region,  and  as  they  under- 
lie the  Horsetown  elswhere,  it  is  evident  that  the  Jurassic  shore- 
line at  this  point  must  have  been  at  least  as  far  west  as  the 
present  shoreline. 

A  second  cause  for  the  lack  of  communication  between  the 
two  provinces  may  lie  in  the  position  of  the  ocean  currents. 
The  Californian  currents  coming  from  the  west  along  a  line  lying 
between  the  Queen  Charlotte  Islands  and  the  island  of  Vancou- 
ver turns  south  at  some  notable  distance  from  the  coast,  and 
after  passing  Vancouver  bears  toward  the  coast  and  flows  on 
along  the  Californian  province.  The  North  Pacific  current  which 
flows  east  closely  parallel  to  the  Californian  bears  northward 
before  reaching  the  Queen  Charlotte  Islands.  Neither  of  these 
currents,  since  they  do  not  cross  the  line  separating  the  two 
provinces,  is  effective  in  establishing  communication  by  carrying 
embryonic  or  larval  forms  which  might  under  different  cir- 
cumstances be  brought  within  their  reach.  This  same  distribu- 
tion of  ocean  currents  probably  held  during  Jurassic  times,  as  in 
general,  the  large  land  masses  in  this  region,  at  least,  had  their 
present  distribution. 

The  attractive  feeding  ground  furnished  by  the  epicontinental 
sea  doubtless  exerted  its  influence  to  prevent  southern  migra- 
tion. When  later  the  waters  were  drawn  off  the  continent  the 
accumulation  of  the  great  numbers  of  organisms  on  the  coast 
may  have  been  sufficient  to  force  the  migration  southward.  Or 
perhaps  the  interval  of  time  was  sufficiently  long  for  some  of 
these  northern  species  to  have  forced  their  way  into  the  Califor- 
nian province  during  later  Jurassic  time.  In  either  case  we 
would  have  in  the  Upper  Jurassic  faunas  of  California  a  north- 
ern element,  and  this  seems  a  well-established  fact.  Neverthe- 
less, since  this  Upper  Jurassic  fauna  has  been  reported  from 
Mexico  it  is  evident  that  communication  was  freer  between  the 
two  provinces  after  the  withdrawal  of  the  waters  of  the  epiconti- 
nental sea.  And  it  is  very  likely  that  the  movement  which  caused 

'See  map  p.  271. 


^ 


-"iWffr4iti*i 


II  ittiiiii  ii'iiil  Vrini        il  iiiMii 


i 


Fig.  3.-Map  showing  the  approximate  position  of  the  Chico  (C)  and  Horsetown 
(H)  Shore  lines  (after  Diller  and  Stanton). 


973 


jr.  A'.  LOGAN 


Fio.   4.— Map  showing   the   position   of   the   North   Pacific  Currents   and  the 
approximate  outline  of  the  Jurassic  Sea. 


m. 


,,^gi^iii,tiit;^ijitim^^ 


ErtCO.VUNEXTAI.  S/.A   OF  Jl'HASSli    AC/-: 


273 


nd  the 


thr  withdrawal  also  slij(lit^ly  depressed   the   barrier  between   llu; 
provinces, 

Fimii  conclusions. — It  now  remains  to  state  briefly,  in  review. 
the  conclusions  to  whi*  h  the  lines  of  investiK-'ition  have  led. 
They  are  as  follows:  .  The  Jiitassic  formation  of  the  interior 
province  of  North  America  was  not  deposited  in  a  body  of 
water  of  even  moderate  oceanic  depth,  but  in  a  shallow  epiconti- 
nental sea. 

2.  This  sea  had  but  one  connection  with  the  ocean  and  that 
connection  was  with  the  North  Pacific  in  the  Queen  Charlotte 
Island  region  ;  in  general  the  outlines  of  the  sea  were  as  indi- 
cated on  the  map  accompanying  this  article. 

3.  There  was  a  connection,  during  this  epoch,  between  the 
Arctic  and  Pacific  by  way  of  the  Bering  waters,  and  by  this 
means  circumpolar  and  Pacific  fauna!  communication  was  estab- 
lished. 

4.  The  Jurassic  deposits  of  the  interior  contain  but  one  fauna 
and  if  more  than  one  period  of  time  is  represented  it  is  not  indi- 
cated by  a  change  in  the  fauna. 

5.  The  fauna  of  the  interior  is  closely  allied  to  the  Cardio- 
ceras  fauna  of  northern  Eurasia. 

6.  Physiographic  rather  than  climatic  condition  restricted 
communication  between  the  Californian  and  interior  provinces. 

7.  Nothing  connected  with  the  history  of  this  Jurassic  sea  or 
its  faunal  relations  is  inimical  to  the  view  that  during  this 
epoch  the  North  American  continent  had,  in  general,  its  present 

outline. 

8.  The  geographic  distribution  of  land  and  water,  as  postu- 
lated by  Neumayr  for  this  period,  is  not  supported  by  the  facts, 
in  so  far  as  the  North  American  Jura  is  concerned. 

W.  N.  Logan. 


